Bump version number.

As we have new features in the upcoming release, we have to bump the
minor release number, not only the bugfix number.

CHANGES.rst

 Changes
 =======
 
-0.5.1.dev0 (unreleased)
------------------------
+0.6.dev0 (unreleased)
+---------------------
 
 - Officially support Pyhthon 3.5.
 - Tests do not depend on `pytest-cov`, `pytest-xdist` anymore.

setup.py

@@ -43,7 +43,7 @@ docs_require = [
 
 setup(
     name="diceware",
-    version="0.5.1.dev0",
+    version="0.6.dev0",
     author="Uli Fouquet",
     author_email="uli@gnufix.de",
     description=(